Thanks guys
How much does the no run no drip shrink? I will definitely try and pick some up before I attach the fins onto my Photon Disruptor.
Would the Lepage that I have been using still be good to use for applying the fins and other gluing other parts? My method so far has been to put some on and then to put a couple of drops of CA along the length to quick tack the fins in place. The Lepage doesn't have what I would consider quick tack, although if you apply a bit of friction between parts it starts to tack up firm really quickly.
Not familiar with Lepage... assuming it's similar to Aileene's Tacky Glue or something similar... should be okay... is it PVA (white) glue?? The only thing you really want to stay away from, IMHO, is school glue and CA (super glue). School glue is pretty weak and soft, not worth the trouble because it'll fail when you need it most, and CA is just a mess for construction-- it has it's place, but not for "structural parts" IMHO... I like CA to harden balsa parts like nosecones and transitions, and for tacking on little detail parts and "greebles" on scale and fantasy-type rockets... but for structural, load bearing joints, IMHO the stuff is awful. CA doesn't age well-- it becomes brittle over time. CA is also particularly weak in the SHEAR plane-- CA's greatest strength is in TENSION, when two parts are trying to pull straight apart away from each other. Unfortunately, MOST of the loads on our fins are shear or translational-- IOW, when the rocket takes off, the wind is pushing on the leading edge and trying to rip the fin off, assisted by gravity and multiple-gees of acceleration. In flight, as the fins stabilize the rocket, the wind is pushing the fins from the side, trying to "lay them over" onto the tube, forces which must be transferred into the tube to turn the direction of flight of the rocket. On landing, usually the fins hit first (on most "standard" type designs) on the rear, outward tip edge, and have to bear the force of suddenly stopping the descending rocket, which is a particularly strong SHEAR FORCE jolt... particularly the weakest type of joint for CA and the most likely point that it will break. CA also seals off the pores of the balsa wood, as it is easily drawn into the wood pores by capillary action where it rapidly "kicks off" due to the limited moisture present in the wood. Once the pores are sealed off, wood glue cannot penetrate them to get a good bond with the wood. Therefore, CA will weaken the glue joint by limiting the ability of the wood glue or white glue to get a good, deep bond with the wood itself. It's about like trying to glue plastic together with wood glue-- the wood glue (or white glue) cannot penetrate, so therefore the bond is extremely weak...
I'd recommend dumping the CA altogether for attaching fins. I know some people do this "mixing glue" stuff but it's a really weird process and I simply cannot fathom how it works worth a rip... the two products are basically incompatible, especially when it comes to making the strongest joints possible from either of them.
If you want the convenience of "instantly attached fins", use the DOUBLE-GLUE JOINT method. Here's how. Get an egg carton from the refrigerator (once you're out of eggs, instead of tossing it, save it-- it's a handy rocket tool!) Invert the foam egg container so it's upside down, and then using your hobby knife, cut slits across the egg cups perpendicular to the long axis of the egg carton. These will make dandy clamps to hold your fins for the double glue joint first application. Once you have your fins ready to glue on the rocket, take them one by one and apply a bead of glue evenly (but not too thick or thin, just a nice, smooth, slightly rounded bead) to the root edge, and spread it evenly with your finger... rake any excess glue on your finger back gently onto the bead so it's smooth, the root edge completely covered, and slightly rounded. Pinch the egg cup in the carton bottom slightly and the cut slit will open up slightly, and slide the fin in carefully, root edge up and level, so the wood glue doesn't run to either end of the fin root. Repeat for all the other fins. Now take the rocket body tube-- you should have all your "fin lines" drawn on the tube in their proper spots, and if the fins are forward of the rear edge of the body tube, reference or hash marks to show their location on the body tube at the rear and/or front edge of the fins. I also highly recommend you lightly sand the body tube with 220 grit sandpaper along the fin line and about 1/8 inch or so on either side of it, to rough up the glassine and maximimize the bond strength of the wood glue. Now, apply a similar thin, even bead of wood glue to the fin line where the fin will attach, and spread it thinly and evenly with your finger where the fin will mount, and slightly wider than the fin (where the fillets will be. It doesn't have to be perfect, but it should be thin and even. You can smooth the glue out by wiping the tube very lightly with your fingertip toward the fin line, so that the glue is slightly thicker over the fin line, and feathered out smooth and flush to the surface at the edge of the sanded areas of the glassine. Wipe any excess glue off your finger onto a paper towel between fin applications. You can do them all at once, since you basically just want a THIN, EVEN coat of glue. Set the tube aside to dry; the "saddle" between the egg cups of a second egg carton (assuming there's not enough room on the first) is ideal... just make sure the glue areas overhang the end of the carton so the tube isn't glued to it.
Let the glue dry for about 20-30 minutes, at a minimum you want the glue extremely tacky (nearly dry). Overnight or longer won't hurt anything... an hour works well. Now, apply a SECOND thin, EVEN coat of glue to the fin root edge. Take the fin and tube and carefully align all the marks BEFORE touching the fin to the tube. Carefully lower the fin down til it touches the tube, and make sure all your marks are properly aligned with the fin-- make any necessary adjustments very quickly, and hold the fin in place for 20-30 seconds, lightly pressing it to the tube. The fin will almost INSTANTLY stick to the tube, and in 20-30 seconds it will be WELL bonded to the tube. Any little droplets of glue squeezed out from under the root edge can then be smoothed out with your fingertip into a mini-fillet-- I sometimes add a very thin little bead of yellow wood glue on either side and spread it very thin and evenly with the droplets squeezed out, to make a very thin, small, even, smooth fillet. You can now move on to the next fin. I usually do mine in pairs (on four-finned rockets) and then use clothespins to clamp them to a flat strip of balsa or something to ensure they're on straight. Let this dry an hour or so, and you can do the next pair of fins. For three-finned rockets, the old "eyeball trick" is good enough.
Once the fins dry overnight, a quick fillet on each side of every fin is quickly and easily done with TMTG... takes all of two minutes to do all the fillets, and set the rocket aside to dry for a few hours or overnight, and it's ready for primer...
How strong are these double-glue joints?? Stronger than either the balsa or the paper tube! Stronger even than a papered balsa fin... I once had a two-stage rocket that the upper stage went wonky after ignition... it spiralled out of control and ended up hitting the ground flat under thrust-- ie on its side, FIN FIRST (fin down). It hit at probably better than 100 mph I would estimate, with some forward velocity and downward at high speed, hit the ground, bounced back up to about ten feet high, and took off straight in "cruise missile" mode (we think it was thrust vectoring by a bad nozzle on the motor caused this weird flight). The fins were 1/8 balsa that had been papered using my "taco shell" method, with white glue and regular printer paper. The fin that hit the ground and absorbed all the impact force of the rocket, on hard clay, had its outer and forward 1/4 to 1/3 of the fin completely disintegrate into balsa and paper dust-- it was just GONE, from the initial impact... as the rocket kept moving, it eventually sheared the fin off the tube... BUT, the glue joint had NOT turned loose, nor the balsa broken... instead, the outer layer of the tube, glassine, and underlying paper layer ply, had ripped completely off the tube on either side of the fillet edge... the fillet and the glue joint itself was still PERFECTLY INTACT! Had the fin not been partially destroyed, I could have just applied a goodly layer of white glue and glue it RIGHT BACK ON the side of the rocket over the exposed underlying layers of paper tubing beneath it from which it was torn. As it was, I had to make a new fin (no biggie, cut one from a pattern and spare balsa, sanded and papered it, and built up the area with a few light thin applications of wood glue, then glued the new fin on. A little sanding and painting and it was like it never happened.
When your glue joint is stronger than the materials being joined, there's NO POINT in trying to go STRONGER... the tube or the fin will break before the fin breaks off, so that's not the weakest link, and any chain always breaks at the weakest link first.
Try it, I think you'll really like it... I know I was VERY skeptical of this method when I first read it as a teenager in G. Harry Stine's "Handbook of Model Rocketry"... I thought it was old-fogey stuff, some sort of super-hard way of doing something, and besides, "slathering a thick layer of wet wood glue over the joint HAS to be stronger", right?? Boy was I wrong! First time I tried a double-glue joint, I was sold... a real "slap to the forehead" sort of moment.
Keep your CA for tacking detail (non-structural non-load bearing) parts and for hardening balsa cones and transitions... wood glue BY FAR makes the strongest joints between wood/wood and wood/paper... white glue is best for paper/paper joints, BTW...
Later and good luck! OL JR